The present invention relates to a reflection illumination device for an object to be illuminated, which is placed in front of the object to display the object with reflected light, and improves display quality by preventing diffused reflection of external light.
As an illumination device for illuminating an object such as a liquid crystal display apparatus, a device having the following arrangement is known. In this illumination device, a light guide is placed in front of the object, a light source such as an LED is placed at a side surface of the light guide, and a reflecting mirror is placed behind the object. In this arrangement, illumination light from the light source which is totally reflected by the surface of the light guide is reflected by the reflecting mirror to display the object on the surface of the light guide.
FIG. 5 shows a known liquid crystal display apparatus using such a reflection illumination device. Referring to FIG. 5, reference numeral 2 denotes a light guide; 10, a liquid crystal display apparatus as an object; 6, a light source, and 9, a reflector plate.
The illumination device in FIG. 5 will be described. First of all, illumination light S emitted from a light source 6 travels in the light guide 2 while repeatedly undergoing total reflection at flat portions on the upper- and lower-surface sides of the light guide 2. The illumination light S incident on an inclined surface 4 of each projection 3 formed on the surface of the light guide 2 changes its direction to a direction perpendicular to the light guide 2 (the vertical direction of the drawing surface of FIG. 5), passes through the light guide 2, and reaches the reflector plate 9 through the liquid crystal display apparatus 10. The illumination light S is reflected by the reflector plate 9, passes through the liquid crystal display apparatus 10 and light guide 2, and emerges outside from the surface of the light guide 2. With the above operation, the contents displayed on the liquid crystal display apparatus 10 are projected on the surface of the light guide 2.
Such a reflection illumination device can illuminate an object by using external light such as sunlight or light from an indoor lamp, and hence has advantages, e.g., low power consumption and allowing a reduction in equipment size.
However, the following problems are posed in the above conventional reflection illumination device.
The problems will be described with reference to FIG. 6. The first problem is that unnecessary reflected light makes it difficult to see part of the contents displayed on the liquid crystal display apparatus. An external light beam R1 incident on a flat portion of the surface of the light guide 2 passes through the light guide 2 and liquid crystal display apparatus 10, without changing its optical path, and is reflected by the reflector plate 9. As a consequence, the contents displayed on the liquid crystal display apparatus 10 are displayed on the surface of the light guide 2. On the other hand, an external light beam R2 incident on the inclined surface 4 of the projection 3 reaches the opposing inclined surface 4 upon changing its traveling direction, and is reflected by the inclined surface 4 to enter an eye of a user in front of the light guide 2 upon further changing its direction. According to the prior art, therefore, unnecessary reflected light of the external light beam R2 makes it difficult to see part of the contents displayed on the liquid crystal display apparatus 10.
The second problem is that the contents displayed on the liquid crystal display apparatus illuminated with light vary in brightness depending on the display positions, resulting in luminance irregularity. The illumination light S emitted from the light source 6 travels in the light guide 2 while being repeatedly reflected. For this reason, as the distance from the light source 6 increases, the brightness of the illumination light S decreases, resulting in luminance irregularity, i.e., different luminances at different portions of the light guide 2. As a consequence, the contents displayed on the liquid crystal display apparatus 10 illuminated with light vary in brightness depending on display positions, resulting in luminance irregularity.
It is, therefore, a principal object of the present invention to provide a reflection illumination device for an object to be illuminated, which can obtain high-quality display by preventing external light reflected by the surface of a light guide from entering the eyes of a user, and a reflection illumination device for an object to be illuminated, which can obtain high-quality display that is bright throughout the display and free from luminance irregularity.
In order to achieve the above object, according to the present invention, there is provided a reflection illumination device comprising a light guide placed in front of an object to be illuminated, a light source arranged around the light guide, and a reflecting mirror placed behind the object, wherein one or a plurality of total reflection areas on which projections or recesses each having a triangular cross-section and serving to totally reflect light emitted from the light source toward the object are formed and arranged on a surface of the light guide, each of the projections or recesses is constituted by an inclined surface inclined at a predetermined angle toward a reference portion positioned at a predetermined position on the light guide, and a vertical surface vertical to the light guide, and the light source or irradiation means for parallelly irradiating the total reflection area with light from the light sources are arranged at an edge of the light guide in correspondence with the total reflection area.